Solar lighting is often used
for solar garden lights, since lamps in the garden are exposed to sunlight
throughout the day. Since a renewable energy source is used, electric
power is saved, no electric wiring is required and there is no
problem of electric shock from exposed cables during the rains.

Solar lighting usually consists of solar
cells , batteries, LEDs and associated electronic circuitry. Several
solar cells are connected together to generate sufficient voltage and
current to charge the batteries. The solar energy is usually stored in
NiCad (Nickel Cadmium) or NimH (Nickel metal hydride) batteries during the
day.

A diode in the solar lighting circuit prevents the current from the
battery flowing through the solar cells at night. After exposure to more
than 5 hours of direct sunlight, the batteries of the solar light
are fully charged and charger electronics prevents overcharging

At
night, the photo resistor (photocell) in the solar lighting turns on the
LED and the energy stored in the batteries is discharged at night. Unlike
conventional batteries used in cars, the batteries used for solar lighting
are deep discharge batteries and can withstand several cycles of
charging and discharging. The LEDs used in solar lighting consume very
little power and the light output is similar to that of candles.

Solar lighting is not widely used since monocrystalline silicon which
is used for manufacturing photovoltaic (solar) cells is still expensive.
The light output depends on location of the solar cell and weather
conditions. On a cloudy day, less energy is stored in the batteries. Also
the LED light output is the maximum in the first few hours of
operation at night and gradually decreases. The battery used for solar
lighting usually has to be replaced after a year, but the LED and solar
cells work for several years.

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